The present invention relates to imaging systems, and in particular to a panoramic camera having a high-precision mirror mounting system.
Mechanical assemblies commonly include components having planar surfaces that require alignment. For example, optical assemblies often include mirrors that must be accurately positioned to provide proper imaging functionality. Typically, proper positioning of each mirror depends on the alignment of the reflective surface of the mirror with a planar reference surface in a base structure. In a conventional optical assembly, this alignment operation is generally performed using a combination spring-hook and adjustment screw mechanism.
For example, FIG. 1 shows a cross section of a conventional optical assembly 100, which includes a mirror 110, a base structure 130, retaining hooks 140a and 140b, guide posts 141a and 141b, extension springs 142a and 142b, and adjustment screws 160a and 160b. Mirror 110 comprises a reflective surface 111 formed on the top surface of a glass substrate, and is therefore called a xe2x80x9cfront surface mirror.xe2x80x9d Because reflected light rays do not have to pass through a layer of glass (as they would in a second surface mirror, i.e., a mirror in which the reflective surface is formed on the bottom surface of the glass substrate), undesirable aliasing and refraction effects are avoided. Base structure 130 includes a planar reference surface 131 that specifies the target plane for reflective surface 111; i.e., the plane in which reflective surface 111 must lie for mirror 110 to provide accurate imaging.
Adjustment screws 160a and 160b are installed in, and extend through, threaded holes 132a and 132b, respectively, in base structure 130. Retaining hooks 140a and 140b are slidably coupled to base structure 130 by guide posts 141a and 141b, respectively, and are attached to base structure 130 by extension springs 142a and 142b, respectively. When retaining hooks 140a and 140b are hooked over the edges of mirror 110, mirror 110 is held firmly against the protruding tips of adjustment screws 160a and 160b by the retentive force of extension springs 142a and 142b. Adjustment screws 160a and 160b can then be used to adjust the vertical position and angular orientation of mirror 110, so as to align reflective surface 111 with reference surface 131 of base structure 130.
Unfortunately, the conventional mirror positioning technique of optical assembly 100 is subject to two significant limitations. First, it is difficult to verify the proper positioning of mirror 110. Even though reflective surface 111 may appear to be aligned with reference surface 131 to the naked eye, even a slight amount of skew between the two surfaces can lead to significant imaging errors in sensitive or high resolution optical assemblies. Therefore, the manual alignment process required by optical assembly 100 can require a time-consuming iterative calibration sequence (i.e., adjust positioning, then test, then adjust based on results, and so on).
Secondly, optical assembly 100 requires recalibration whenever mirror 110 is replaced, due to the fact that mirrors are generally not held to tight thickness tolerances. While base structure 130 is typically made from a readily machinable material and can therefore be milled to highly accurate dimensions, lapping a glass component (such as a mirror substrate) to a precise thickness can be difficult and expensive. Therefore, if mirror 110 is replaced, adjustments will have to be made to screws 160a and 160b to accommodate the new mirror thickness. In addition, even if mirror 110 is simply removed and then reinstalled, play between the threads of adjustment screws 160a and 160b and threaded holes 132a and 132b, respectively, may necessitate a recalibration.
Accordingly, it is desirable to provide a system for accurately and repeatably aligning planar surfaces of components in a mechanical assembly that does not require an iterative calibration procedure and can accommodate deviations in the non-planar dimensions of the components.
The present invention provides a planar surface alignment system that uses the planar surfaces themselves to perform the alignment, thereby ensuring accurate positioning while eliminating the need for calibration. According to one embodiment of the present invention, a first planar surface of an auxiliary component is aligned with a reference planar surface of a base component by a retaining element having a base contact region and an auxiliary contact region. The base contact region and the auxiliary contact region are coplanar portions of the retaining element. The base contact region is clamped against the reference planar surface, and the first planar surface is held against the auxiliary contact region by a resilient force. Therefore, the base contact region is aligned with the reference planar surface, and the first planar surface is aligned with the auxiliary contact region. Because the auxiliary contact region and the base contact region are coplanar, the first planar surface is aligned with the reference planar surface.
In another embodiment of the present invention, a front surface mirror is mounted on elastic pads in a well in a base structure. The elastic pads are configured to displace the planar reflective surface of the front surface mirror away from the planar reference surface. Retaining clips having coplanar contact regions are screwed to the base structure such that portions of the coplanar contact regions are clamped against the planar reference surface, and other portions of the coplanar contact regions contact the planar reflective surface. The elastic pads deform in response to the loading from the retaining clips, allowing the contact regions to position the planar reflective surface. In this manner, the planar reflective surface is aligned to the planar reference surface via the contact regions of the retaining clips.
According to another embodiment of the present invention, the elastic pads are formed from an elastomer or other resilient material, and can have any desired cross-section. The elastic pads can be placed under all edges of the front surface mirror, or can be placed at selected locations. The elastic pads can be attached to the front surface mirror, to the base structure, or can be a completely separate component of the optical assembly. According to another embodiment of the present invention, the elastic pads can be replaced with a resilient support structure using mechanical springs. Alternatively, gas or hydraulic cylinders can be used to provide the resilient force.
According to another embodiment of the present invention, the retaining clips comprise straight elements positioned over two opposite edges of the mirror. According to another embodiment of the invention, the retaining clips comprise a plurality of smaller elements positioned at various intervals around the perimeter of the mirror. According to another embodiment of the present invention, a single retaining clip clamps along the entire perimeter of the mirror. According to another embodiment of the present invention, the screwed-down retaining clips can be replaced with retaining elements are hinged to the base structure and pulled tight against the planar reference surface by springs. According to another embodiment of the present invention, the screwed-down retaining clips can be replaced with retaining elements that are clamped against the planar reference surface by mechanical latching mechanisms.
According to another embodiment of the present invention, a camera system includes multiple camera-mirror arrangements, each camera being aimed at its associated mirror, the mirror directing the camera field of view away from a central axis of the camera system. Each of the mirrors is mounted in a resilient mounting structure, and clamped in place by a set of retaining clips. Each retaining clip in the set includes a coplanar contact region that spans a planar reference surface and a portion of the reflective surface of the mirror. Because the resilient mounting structure holds the mirror against the retaining clips, the reflective surface of the mirror is aligned with the planar reference surface. According to an embodiment of the present invention, the outward facing camera system comprises an eight-sided camera system.
The present invention will be more fully understood in view of the following description and drawings.